The present invention is related to headrests for motor-vehicle seats comprising a yielding body, a pair of parallel support rods lowerly projecting from the yielding body, and height adjustment means of the yielding body relative to a seat backrest, including a series of positioning notches provided along each of said support rods and respective resilient locking members normally engaging in a disengageable fashion said positioning notches.
Traditionally, height adjustment of the yielding body in headrests of the above-referenced type is performed through provision of two different systems: in a first case the support rods are slidably fitted within respective tubular portions, spaced apart from each other and oriented substantially vertically, of a load bearing framework incorporated within the yielding body, as disclosed for instance in FR-A-2577869 in the name of the same Applicant. In a second case the support rods, rigidly connected to the load bearing framework fitted in the yielding body, are slidable in a substantially vertical direction through a pair of tubular guide elements which in turn are to be rigidly connected to the structure of a seat backrest, as disclosed for instance in EP-A-0582765 and in European Patent Application No. 96830573.0, unpublished at the priority date of the present application, both also in the name of the same Applicant.
In both cases an inconvenience is experienced consisting of that, should the vehicle on board of which the headrest is mounted be subjected to a heavy crash, the yielding body may have a tendency to accidentally displace upwardly, due to spontaneous sliding in the first case of the yielding body itself relative to the support rods, and in the second case of the support rods along the tubular guiding elements. In such event the primary function of the headrest, i.e. reaction afforded by the yielding body against rearward motion of the user's head, is jeopardized. This drawback is particularly critical in connection with short users, and anyway whenever upward displacement of the yielding body in case of crash be such as to produce complete withdrawal thereof from the support rods or, respectively, to produce complete extraction of the support rods from the related tubular guide elements.